@misc{SMPP,
  title={{Short Message Peer to Peer Specification v3.4}},
  author={{SMS Forum}},
  howpublished={\url{http://www.smsforum.net/}},
  year={2003}
}

@misc{InAppOverview,
  title={{In app Billing Overview}},
  author={{Google}},
  howpublished={\url{http://developer.android.com/guide/market/billing/billing_overview.html/}},
  year={2011},
  month={may}
}